node-mssql - Connection is closed - sql-server

Question

I use node typescript with mssql library to insert data into tables in my Azure server. I create a global connection pool, init it in the constructor then connect to it from route service. However, it shows the error
ConnectionError: Connection is closed at ActionService.insertion", "...at new ActionService", "... at new AppDataServices".
I don't know where broke down my logical connection between the global pool and route service. My SQL query might be wrong, but the main thing is about connection to the database.
Below is my code:
app-data-services.ts (global connection pool):
import * as mssql from 'mssql';
import { AppConfig } from '../config';
import { ActionService } from './data-services';
import { Logger, LoggerFactory } from '../common';
export class AppDataServices {
private static readonly LOGGER: Logger = LoggerFactory.getLogger();
private db: any;
public actionService: ActionService;
constructor(private appConfig: AppConfig) {
this.initConnectionPool();
this.actionService = new ActionService(this.db, AppDataServices.LOGGER);
}
private initConnectionPool() {
this.db = new mssql.ConnectionPool({
user: this.appConfig.mssqlUsername,
password: this.appConfig.mssqlPassword,
server: this.appConfig.mssqlServer,
database: this.appConfig.mssqlDatabase,
// If you are on Microsoft Azure, you need this:
options: { encrypt: true }
}, (err: any) => {
if (err) AppDataServices.LOGGER.error('MSSQL error', err);
});
}
}
action-service.ts (route data service):
import * as mssql from 'mssql';
import { Logger, LoggerFactory } from '../../../common';
export class ActionService {
private static readonly LOGGER: Logger = LoggerFactory.getLogger();
constructor (private db: any, private logger: any) {
this.insertion();
}
insertion() {
const request = new mssql.Request(this.db);
request.query(
`
INSERT INTO dbo.action
(timestamp, result, description, request_endpoint, request_payload, response_status, response_payload, actualAmount, rule_id, lendbook_id)
SELECT t1.start, 'SUCCESS', NULL, '/lendbook/usd', NULL, '200', NULL, t1.originalAmount, t1.id, t2.id
FROM dbo.rule t1, dbo.lendbook t2
INNER JOIN t2.id = t1.id
`, (err, result) => {
if (err) {
console.error(err);
return;
}
return result.recordsets[0];
});
}
}